Smectic layer rotations in ferroelectric liquid crystals (FLC) upon application of electric fields have been observed only in chiral smectic phases and believed to be related to the electroclinic effect. In this article, effects of electric field shape and frequency on smectic layer rotations in siloxane-based FLCs were investigated by applying various kinds of asymmetric ac waveforms for a range of frequencies and temperatures. For a given peak voltage, we have found that the asymmetry was one of the most important parameters and demonstrated that the modified step form showed the best efficiency for smectic layer rotations.